Radiation is not only highly related to our daily life but also exist everywhere. For example, both cosmic ray and earth radiation are natural background radiations and differ with geography and geology. Besides the natural background radiation, the radiation sources caused from human, such as nuclear power, radio diagnosis, radiotherapy and nuclear medicine, are also broadly applied for human's life.
According to the data published by National Health Administration in 2010, cancer is still the top reason of death. The percentage of death caused by cancer is 28.4, and it is obviously that cancer threatens human's health. To date, surgery, chemotherapy and radiotherapy are the main methods for treating cancer.
The principle of radiotherapy is to use a high energy radiation, such as an indirectly ionizing radiation, to ionize or excite atoms that compose tumor cells when it reacts with the tumor cells and further produce toxic free radicals to destroy the tumor cells; tumor cells can be destroyed also by radiation energy released by a directly ionizing radiation which causes single- or double-strand breaks within the deoxyribonucleic acids of tumor cells. As to the dose of the therapy prescription, it is based on a complicated treatment plan to evaluate the absorption radiation dose of the tumor cells and the normal tissues, and the results are further provided to doctors to verify the feasibility and anticipated effects. When the medical team confirms the treatment plan, the irradiation parameters will be sent to the instrument. Also, the quality of the irradiation beam will be checked regularly to insure that the differences between the therapy prescription and the dose absorbed by patients are within an acceptable error. After a plurality of irradiations, patients complete their treatment. The effect of radiotherapy is based on the theory of radiation biology. The dose-response curve shows that the greatest slope resides in the middle of the curve, and a change of 5% in dose will affect the tumor control probability by 10% to 20%, and the normal tissue complication probability by 20% to 30%. Therefore, the accurate dose delivery is very important in radiotherapy.
Most of the common medical radiotherapy equipment are high-energy linear accelerators (LINACs), such as high energy X-ray therapy machines of 6 MV, 10 MV, 12 MV or 18 MV. In addition, more advanced radiotherapy modalities, such as proton therapy, carbon ion therapy and boron neutron capture therapy, are also developed to fight against cancers and to increase the patient survival rate. Therefore, radiotherapy should accompany more deliberate plans for quality control and dose verification to assure the treatment quality for patients.
Radiochromic film contains special chemicals to react with radiation and let the chemicals undergo energy level change. And then, an observable color change of the radiochromic film will emerge as a result of polymerization or other coloration reactions. The radiation dose can then be estimated through a coloration degree of the colorization. As shown in FIG. 1, a conventional radiochromic film, such as GAFCHROMIC® External Beam Therapy 2 (EBT2) film 100 produced by International Specialty Products Inc. (USA), is widely used for clinical dose delivery verification. Its structure described from bottom to top contains a base 10, an active layer 20, a surface layer 30, an adhesive 40 and a top 50. However, the film as mentioned above still has a plurality of limitations. For example, it is mostly used to measure the photon dose in a photon radiation field rather than being used to measure the dose in a mixed one.